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Briefing at AAAS: Experts Question Motives, Value of U.S. Satellite Shoot-Down
Geoffrey Forden (left) and Jeffrey Lewis (r)
The Navy's recent shoot-down of a crippled U.S. spy satellite may have been undertaken for questionable policy reasons and complicates efforts to restrain the development of anti-satellite weapons, two defense policy specialists said at a AAAS-hosted news briefing.
Pentagon officials said the 20 February shoot-down of the non-functioning satellite was necessary to prevent the craft from crashing to Earth and potentially spreading toxic hydrazine fuel.
But Jeffrey Lewis, an arms control specialist at the nonprofit New America Foundation, said the administration of U.S. President George W. Bush has not provided the risk calculations and other data needed to independently verify that the shoot-down was necessary. He spoke at an 18 March briefing at AAAS organized by the Center for Media and Security and the AAAS Center for Science, Technology, and Security Policy.
Lewis called the satellite shoot-down "a fascinating case-study in how one can sort of justify a preferred policy position without paying very much attention to the facts at hand." Some critics suspect the administration undertook the shoot-down primarily to test an anti-satellite weapon, a charge Pentagon officials have denied. They said the hydrazine tank aboard the satellite, had it plummeted intact to Earth, could have vented gases that posed a real threat to individuals in the immediate vicinity of the impact.
But Lewis is skeptical and said none of the relevant risk-calculations have been made public, including the odds that the satellite could have come down in a populated area, the chances that the hydrazine fuel tank would have survived re-entry, and the potential health risks had toxic fumes been spread over a specific area.
"One would think this data should be released," Lewis said. "There's no reason to classify it."
A second speaker at the briefing, Geoffrey Forden, a senior research associate in the Security Studies Program at the Massachusetts Institute of Technology, said it is difficult to say whether the hydrazine tank would have made it through the atmosphere without breaking apart. His calculations suggest the re-entry forces might not have been violent enough to destroy the tank and release the toxic gas before it reached the ground. Even if the tank did survive re-entry, however, Forden's calculations suggest the chances of harm were low—about a 3.5% chance that an individual somewhere in the world would be injured or killed.
Given those odds, he said, the more worrisome aspect of the shoot-down may be its longer-term impact on diplomatic efforts to control anti-satellite weapons, or ASATs, with their potential to create huge amounts of orbital debris that could cripple use of near-Earth space for generations.
Forden noted that the only thing that distinguishes the secretive Chinese ASAT test of 11 January 2007 and the U.S. shoot-down of the crippled spy satellite (designated USA-193) is the relative transparency associated with the U.S. action. But unless the Pentagon releases a more detailed explanation of its reasoning for the shoot-down, Forden said, other countries, and China in particular, will use the action as a justification for future ASAT development.
The information released should include details of the simulations of the re-entry of the hydrazine tank, Forden said, including the forces it experienced as it passed through the atmosphere and the heating of the frozen hydrazine on the way down.
China's ASAT has both significant capabilities as well as important limitations, Forden said. A careful study of the debris generated by the January 2007 test shows China used a sophisticated "hit-to-kill" interceptor, equivalent in many ways to the U.S. interceptor used in the destruction of USA-193. The Chinese vehicle was much more sophisticated than the "space-mines" developed by Soviet weapons scientists in the 1980s, he said.
Since China tested its ASAT against a relatively low-altitude target (530 miles), the interception had a very high "closing speed"—the speed at which a target and interceptor approach each other. The higher the closing speed, Forden said, the more difficult the interception. So the Chinese test was the most challenging they could have done. Attacks against higher, more strategically significant targets such as global positioning satellites or telecommunications satellites in geostationary orbits at 22,300 miles, would actually be easier, he said.
But attacks against these higher satellites would require China to launch ASATs on larger missiles that can only be launched from a small number of appropriate launch pads. Since it takes a minimum of two weeks for these larger vehicles to be stacked and assembled out on their pads, the United States would have a significant period of tactical warning. And almost any warning would be sufficient to allow the U.S. to move its satellites out of the way, he said.
Even if the U.S. did not move its satellites when it sees an attack coming, Forden said, it has so many space assets that it could afford to ride out an attack. For instance, if China destroyed all eight U.S. military communications satellites over the Taiwan Strait and the eight most capable U.S.-owned and -operated civilian communications satellites in the area—and 16 satellites is the maximum China could destroy with its current launch pads—Forden estimates the U.S. still would have access to more than four times the communications bandwidth it used at the peak of the Iraq war.
While the United States could ride out an all-out space war with China, Forden said, other regional powers could not. And more importantly, the space debris generated by such an attack could start what has been called a "catastrophic chain-reaction" where debris from one collision hits another satellite causing more debris and so on. Experts have warned that this might create so much space debris that all satellites might be destroyed and space near the Earth rendered unusable for hundreds or even thousands of years.
The Chinese anti-satellite test last year is instructive regarding the potential disruption. Prior to the test, Forden said, there was a 12% chance each year that any given satellite might have to be moved in orbit to avoid collision with a detectable chunk of debris. After the single Chinese test, the chances grew to 18% chance per year that such a maneuver will be necessary. By one account, the test produced at least 2,300 pieces of debris large enough to be routinely tracked by the U.S. Space Surveillance Network. NASA's Orbital Debris Program Office estimated the test produced more than 35,000 pieces of debris down to 1 centimeter in size.
So shooting down USA-193, Forden and Lewis argue, could carry a heavy price over the longer term by legitimizing a Chinese weapon that, if used, might deny space for satellites needed for such humanitarian purposes as weather-monitoring and flood surveillance.
"We have a substantial interest in restraining the testing and deployment of debris- creating ASATs," Lewis said. The U.S. decision to shoot down the defunct spy satellite makes that task harder, he said, even if there were legitimate concerns for human life and health.
Lewis remains confident that outside analysts will continue to do their own risk calculations for hydrazine and try to answer some of the questions being raised. But it is in the Pentagon's interest to provide more data on the rationale for the test and its end results, he said.
"You have to be more transparent to help us prove that the United States wasn't just conducting another ASAT test," he said. "You have to help us prove that there was a real danger."
26 March 2008